Optoelectronic semiconductor chip comprising a multi-quantum well comprising at least one high barrier layer

ABSTRACT

An optoelectronic semiconductor chip including a multi-quantum well including at least one high barrier layer is disclosed. In an embodiment, the chip includes a p-type semiconductor region, an n-type semiconductor region and an active layer suitable for emission of radiation arranged between the p-type region and the n-type region, wherein the active layer is in the form of a multiple quantum well structure. The multiple quantum well structure has a plurality of alternating quantum well layers and barrier layers, wherein a barrier layer arranged closer to the p-type region than to the n-type region is a high barrier layer having an electronic band gap Ehb that is larger than electronic band gaps Eb of other barrier layers, and wherein a quantum well layer that adjoins the high barrier layer on a side facing towards the p-type region has a thickness that is greater than thicknesses of other quantum well layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.14/907,230, entitled “Optoelectronic Semiconductor Chip Comprising aMulti-Quantum Well Comprising at Least One High Barrier Layer” which wasfiled on Jan. 22, 2016 which is a national phase filing under section371 of PCT/EP2014/065750, filed Jul. 22, 2014, which claims the priorityof German patent application 10 2013 107 969.5, filed Jul. 25, 2013, allof which are incorporated herein by reference in its entirety.

TECHNICAL FIELD

The invention relates to an optoelectronic semiconductor chip which hasan active layer in the form of a multiple quantum well structure.

BACKGROUND

In radiation-emitting optoelectronic semiconductor chips, such as, forexample, LED chips or laser diode chips, the emission of radiation isusually dependent upon the operating temperature. Typically a decreasein the efficiency of radiation generation is observable with increasingtemperature. In the case of very high operating temperatures, thereduced efficiency of radiation generation can lead to a significantdecrease in brightness. For example, in the case of radiation-emittingsemiconductor chips that contain an InGaAlP semiconductor material andemit in a wavelength range of from 550 nm to 640 nm, an increase intemperature from room temperature to a temperature of about 100° C. canresult in a decrease in brightness of up to 80 percent if no suitablemeasures are taken to stabilize the radiation emission.

SUMMARY

The invention is based on the problem of defining a radiation-emittingoptoelectronic semiconductor chip which is distinguished by a reducedtemperature dependence of the radiation emission.

According to at least one embodiment, the optoelectronic semiconductorchip comprises a p-type semiconductor region, an n-type semiconductorregion, and an active layer arranged between the p-type semiconductorregion and the n-type semiconductor region, which active layer is in theform of a multiple quantum well structure. The multiple quantum wellstructure has a plurality of alternating quantum well layers and barrierlayers, the barrier layers having a larger electronic band gap than thequantum well layers.

In the optoelectronic semiconductor chip, advantageously at least one ofthe barrier layers of the multiple quantum well structure which isarranged closer to the p-type semiconductor region than to the n-typesemiconductor region is a high barrier layer. A high barrier layer is tobe understood here and hereinbelow as being a barrier layer that has anelectronic band gap E_(hb) which is larger than an electronic band gapE_(b) of the other barrier layers of the multiple quantum wellstructure. In other words, the barrier layers of the multiple quantumwell structure, with the exception of the at least one high barrierlayer, each have an electronic band gap E_(b), while the electronic bandgap in one or more high barrier layers which are arranged closer to thep-type semiconductor region than to the n-type semiconductor region israised to a value E_(hb)>E_(b). To achieve the larger electronic bandgap E_(hb) of the at least one high barrier layer, the at least one highbarrier layer advantageously has a material composition that differsfrom the material composition of the other barrier layers of themultiple quantum well structure. The other barrier layers of themultiple quantum well structure which are not in the form of highbarrier layers advantageously each have the same material compositionand the same electronic band gap E_(b).

The insertion of the at least one high barrier layer in a region of themultiple quantum well structure that faces towards the p-typesemiconductor region has the advantage that the high barrier layer actsas a charge carrier barrier especially for holes. It has been found, inparticular, that it is more difficult for holes to pass through the highbarrier layer than for electrons. The holes injected into the multiplequantum well structure by the p-type semiconductor region thereforecannot disperse unimpeded in the entire multiple quantum well structure,but collect preferentially in the quantum well layer or the plurality ofquantum well layers that are arranged between the p-type semiconductorregion and the at least one high barrier layer. As a result of thisnon-uniform distribution of the holes in the multiple quantum wellstructure, the efficiency of radiation generation declines particularlyat low temperatures, such as, for example, at room temperature. Athigher temperatures, however, it is easier for the holes to pass throughthe high barrier layer in the region of the multiple quantum wellstructure that faces towards the p-type semiconductor region. Withincreasing temperature the holes become distributed more uniformly inthe multiple quantum well structure, so that charge carrierrecombinations for generating radiation take place in a larger region ofthe multiple quantum well structure. For that reason, the decrease inthe efficiency of radiation generation caused by the at least one highbarrier layer is the smaller, the higher the temperature.

In the case of the multiple quantum well structure described herein, adecrease in the efficiency of radiation generation at low temperatures,especially at room temperature, caused by the at least one high barrierlayer inserted into the quantum well structure is deliberately acceptedin order to counteract the reduced efficiency that is typically observedin radiation-emitting semiconductor devices at increasing temperatures.Typically the efficiency of radiation-emitting semiconductor devicesdeclines with increasing temperature, because the confinement of chargecarriers in the active zone becomes poorer as a result of the greatermobility of the charge carriers and accordingly increasing losses occurin the form of non-radiating recombinations outside the active layer.The insertion of the at least one high barrier layer into a region ofthe multiple quantum well structure that faces towards the p-typesemiconductor region gives rise to an opposing effect as a result ofwhich the efficiency of radiation generation increases with increasingtemperature. In that way, a decrease in brightness customarily observedwith increasing temperature is reduced or preferably even compensated.The optoelectronic semiconductor chip is therefore distinguished by animproved temperature stability of the brightness of the emittedradiation.

According to a preferred embodiment, the at least one high barrier layerhas an electronic band gap E_(hb) for which the following applies:E_(hb)−E_(b)≥0.05 eV. The material composition of the high barrier layeris therefore preferably chosen to be such that the high barrier layerhas an electronic band gap at least 0.05 eV greater than the otherbarrier layers. In an especially preferred variant, the electronic bandgap E_(hb) of the at least one high barrier layer is even 0.1 eV greaterthan the electronic band gap of the other barrier layers.

The multiple quantum well structure preferably has not more than 10 highbarrier layers. The number of high barrier layers in the multiplequantum well structure is preferably between 1 and 10, especiallypreferably between 1 and 5.

In one embodiment of the optoelectronic semiconductor chip, the first kbarrier layers of the multiple quantum well structure starting from thep-type semiconductor region are high barrier layers, where k is a numberbetween 1 and 10 and especially preferably between 1 and 5.

In a preferred embodiment, the multiple quantum well structure has justone high barrier layer. With the exception of the just one high barrierlayer, preferably all other barrier layers each have the same band gapE_(b). The insertion of just one high barrier layer has the advantagethat the efficiency of radiation generation at room temperature isreduced to a lesser extent than when a plurality of high barrier layersis used.

When just one high barrier layer is used, that layer is preferablyarranged between a quantum well layer that is the m^(th) quantum welllayer starting from the p-type semiconductor region and the immediatelyadjacent quantum well layer, where m is a number between 1 and 20,preferably between 1 and 10. In other words, in such an embodimentbetween 1 and 20, preferably between 1 and 10, quantum well layers arearranged between the p-type semiconductor region and the high barrierlayer, and all other quantum well layers are arranged between the highbarrier layer and the n-type semiconductor region. In the case of lowoperating temperatures, the holes therefore accumulate preferentially inthe m quantum well layers between the p-type semiconductor region andthe high barrier layer.

In such an embodiment, in particular m=1 can hold true. In that case,the high barrier layer is arranged between the first quantum well layerand the second quantum well layer, starting from the p-typesemiconductor region. In such an embodiment, therefore, only theoutermost quantum well layer of the multiple quantum well structure isseparated from the other quantum well layers by means of the highbarrier layer.

In a further embodiment, the multiple quantum well structure has notonly one high barrier layer but a plurality of high barrier layers whichare arranged closer to the p-type semiconductor region than to then-type semiconductor region. When a plurality of high barrier layers isused it may possibly be necessary to accept an even greater decrease inefficiency at room temperature, but this offers the possibility ofreducing or even compensating even greater reductions in brightness athigh temperatures. Accordingly, although the brightness at roomtemperature is significantly reduced in comparison with a multiplequantum well structure without high barrier layers, its temperaturestability is substantially improved.

The multiple quantum well structure can be based on a phosphide compoundsemiconductor, especially In_(x)Al_(y)Ga_(1-x-y)P where 0≤x≤1, 0≤y≤1 andx+y≤1, and be intended, for example, for emission of radiation in thewavelength range of from 550 nm to 640 nm. In the case of optoelectronicsemiconductor chips having such an active layer, the at least one highbarrier layer is especially advantageous, because such optoelectronicsemiconductor chips typically exhibit a strong temperature dependence ofthe emitted brightness, which dependence can be reduced or evencompensated by means of the at least one high barrier layer.

Alternatively, the multiple quantum well structure can be based on anitride compound semiconductor, especially In_(x)Al_(y)Ga_(1-x-y)N where0≤x≤1, 0≤y≤1 and x+y≤1, and be intended, for example, for emission inthe ultraviolet or blue spectral range. Furthermore, the multiplequantum well structure can also be based on an arsenide compoundsemiconductor, especially In_(x)Al_(y)Ga_(1-x-y)As where 0≤x≤1, 0≤y≤1and x+y≤1, and be intended for an emission in the red and/or infraredspectral range, for example, at approximately from 700 nm to 800 nm.

In a preferred embodiment, the at least one high barrier layer and theother barrier layers each comprise In_(x)Al_(y)Ga_(1-x-y)P,In_(x)Al_(y)Ga_(1-x-y)N or In_(x)Al_(y)Ga_(1-x-y)As where 0≤x≤1, 0≤y≤1and x+y≤1, the aluminum content y of the at least one high barrier layerbeing greater than the aluminum content y of the other barrier layers.The greater aluminum content advantageously brings about an enlargementof the electronic band gap of the high barrier layer in comparison withthe other barrier layers.

The number of other barrier layers of the multiple quantum wellstructure that are not configured as high barrier layers and each havethe same electronic band gap E_(b) is advantageously at least 10,preferably at least 20. The number of other barrier layers canespecially be between 10 and 100. The number of other barrier layers isadvantageously at least 5 times and especially preferably at least 10times as great as the number of high barrier layers having the increasedband gap.

In a further advantageous embodiment, at least one quantum well layerthat adjoins the at least one high barrier layer on a side facingtowards the p-type semiconductor region has an electronic band gapE_(lw) that is smaller than the band gap E_(w) of the other quantum welllayers. It has been found that in a quantum well layer that adjoins theat least one high barrier layer on a side facing towards the p-typesemiconductor region, a very high charge carrier density develops as aresult of the barrier action. This can have the result that chargecarrier recombinations also from more highly excited states take place,such recombinations causing emission of radiation of greater energy andaccordingly of shorter wavelength. A resulting shift in the emissionspectrum towards a shorter wavelength can advantageously be reduced oreven entirely compensated if the quantum well layer that adjoins the atleast one high barrier layer has a smaller band gap than the otherquantum well layers.

An alternative way of reducing or compensating the effect of a shift ofthe emission spectrum towards a shorter wavelength is for at least onequantum well layer that adjoins the at least one high barrier layer on aside facing towards the p-type semiconductor region to have a greaterthickness than the other quantum well layers. In a similar way to thereduction of the electronic band gap, an increase in the thickness ofthe quantum well layer also leads to an increase in the emittedwavelength and accordingly to a reduction or compensation of theundesired effect.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail below with reference toexemplified embodiments in conjunction with FIGS. 1 to 6, wherein

FIG. 1 is a diagrammatic view of a cross-section through anoptoelectronic semiconductor chip according to a first exemplifiedembodiment;

FIG. 2 is a diagrammatic view of a cross-section through anoptoelectronic semiconductor chip according to a second exemplifiedembodiment;

FIG. 3 is a diagrammatic view of a cross-section through anoptoelectronic semiconductor chip according to a third exemplifiedembodiment;

FIG. 4 is a diagrammatic view of a cross-section through anoptoelectronic semiconductor chip according to a fourth exemplifiedembodiment;

FIG. 5 is a graph showing the electronic band gap in dependence upon aspatial co-ordinate z running in the perpendicular direction in a fifthexemplified embodiment; and

FIG. 6 is a graph showing the relative brightness B(T)/B(T=25° C.) independence upon the temperature T in an optoelectronic semiconductorchip according to a sixth exemplified embodiment in comparison with aconventional optoelectronic semiconductor chip.

In the Figures, elements that are identical or have identical action aredenoted by the same reference numerals. The elements illustrated and therelative sizes of the elements to one another should not be regarded asto scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The optoelectronic semiconductor chip 10 according to a firstexemplified embodiment shown in FIG. 1 is an LED chip which has a p-typesemiconductor region 4, an n-type semiconductor region 6, and an activelayer 5 suitable for emission of radiation which is arranged between thep-type semiconductor region 4 and the n-type semiconductor region 6. Theexemplified embodiment of the optoelectronic semiconductor chip 10 iswhat is known as a thin-film semiconductor chip from which a growthsubstrate originally used for epitaxial growth of the semiconductorlayers 4, 5, 6 has been detached and instead the semiconductor layersequence has been joined to a carrier substrate 1 different from thegrowth substrate by means of a connecting layer 2, especially a solderlayer. In such a thin-film light-emitting diode chip 10, the p-typesemiconductor region 4 usually faces towards the carrier substrate 1.Between the p-type semiconductor region 4 and the carrier substrate 1there is advantageously arranged a mirror layer 3 by means of whichradiation emitted in the direction of the carrier substrate 1 isadvantageously deflected in the direction towards a radiation exitsurface 11 of the optoelectronic semiconductor chip. The mirror layer 3is, for example, a metal layer that comprises Ag, Al or Au.

For electrical contacting of the optoelectronic semiconductor chip 10 itis possible, for example, for a first contact layer 8 to be provided ona rear side of the carrier substrate 1 and for a second contact layer 9to be provided on a sub-region of the radiation exit surface 11.

The p-type semiconductor region 4 and the n-type semiconductor region 6can each be composed of a plurality of sublayers and need notnecessarily consist exclusively of p-doped layers or n-doped layers, butcan also have, for example, one or more undoped layers.

As an alternative to the exemplified embodiment shown, theoptoelectronic semiconductor chip 10 could also have an oppositepolarity, that is to say the n-type semiconductor region 6 could facetowards a substrate and the p-type semiconductor region 4 could facetowards a radiation exit surface 11 of the optoelectronic semiconductorchip (not shown). This is usually the case in optoelectronicsemiconductor chips in which the growth substrate used for epitaxialgrowth of the semiconductor layers is not detached, because the n-typesemiconductor region is usually grown onto the growth substrate first.

The active layer 5 of the optoelectronic semiconductor chip 10 intendedfor emission of radiation is in the form of a multiple quantum wellstructure 7. The multiple quantum well structure 7 has a plurality ofalternately arranged quantum well layers 71 and barrier layers 72, 73.In the exemplified embodiment shown, the multiple quantum well structure7 has one hundred layer pairs each composed of a quantum well layer 71and a barrier layer 72, 73. The quantum well layers 71 each have anelectronic band gap E_(w). Starting from the n-type semiconductor region6 of the optoelectronic semiconductor chip 10, the first 98 barrierlayers each have an electronic band gap E_(b).

The two barrier layers 73 located closest to the p-type semiconductorregion 4 are each in the form of a high barrier layer 73 having a largerelectronic band gap E_(hb) than the other barrier layers 72. For thatpurpose the high barrier layers 73 differ in material composition fromthe other barrier layers 72. The larger electronic band gap E_(hw) ofthe high barrier layers 73 can have been created especially by the highbarrier layers 73 having a greater aluminum content than the otherbarrier layers 72. For example, the high barrier layers 73 can compriseIn_(0.5)Al_(0.5)P and the other barrier layers 72 can compriseIn_(0.5)Ga_(0.25)Al_(0.25)P.

As a result of the increased electronic band gap E_(hb), the highbarrier layers 73 act particularly as barriers for holes and make itmore difficult for holes from the p-type semiconductor region 4 to passinto the portion of the quantum well structure 7 that faces towards then-type semiconductor region 6. During operation of the optoelectronicsemiconductor chip 10, the concentration of holes in the quantum welllayers 71 that adjoin the boundary faces of the high barrier layers 73facing towards the p-type semiconductor region 4 is therefore higherthan in the other 98 quantum well layers 71 of the multiple quantum wellstructure 7. Particularly at low operating temperatures, this thereforeresults in a non-uniform charge carrier distribution in the multiplequantum well structure 7, which reduces the efficiency of radiationgeneration.

At higher operating temperatures, the holes are able to pass through thehigh barrier layers 73 more easily, so that the charge carrierdistribution becomes more uniform with increasing temperature. In thisway the efficiency of radiation generation rises with increasingtemperature. This effect advantageously reduces or compensates theopposing effect that the efficiency of radiation generation in theactive layer 5 declines with increasing temperature on account of apoorer confinement of charge carriers in the multiple quantum wellstructure 7, as is typically observed in radiation-emittingsemiconductor chips. The optoelectronic semiconductor chip 10 istherefore distinguished by an improved temperature stability of theemitted brightness.

The optoelectronic semiconductor chip 10 shown in FIG. 1 is intended,for example, for emission at a wavelength of 590 nm. It has been foundthat on account of the two high barrier layers 73 the brightness at roomtemperature declines by about 15 percent in comparison with an otherwiseidentical semiconductor chip in which all one hundred barrier layers 72are formed from In_(0.5)Ga_(0.25)Al_(0.25)P. At an operating temperatureof 100° C., however, the optoelectronic semiconductor chip 10 emits thesame brightness as an otherwise identical conventional semiconductorchip in which all the barrier layers have the same electronic band gap.The relative change in brightness with operating temperature istherefore smaller in the case of the optoelectronic semiconductor chip10 according to the exemplified embodiment than in the case of thecomparison example in which all the barrier layers have the sameelectronic band gap.

FIG. 2 shows a further exemplified embodiment of an optoelectronicsemiconductor chip 10 which is intended for emission at a wavelength of615 nm. The optoelectronic semiconductor chip 10 differs from theexemplified embodiment of FIG. 1 in that the multiple quantum wellstructure 7 acting as active layer 5 has fifty layer pairs composed ofquantum well layers 71 and barrier layers 72, 73. In contrast to theprevious exemplified embodiment, only the first barrier layer 73starting from the p-type semiconductor region 4 is configured as a highbarrier layer 73. The high barrier layer 73 contains In_(0.5)Al_(0.5)Pand therefore has a larger electronic band gap than the 49 other barrierlayers 72, which each comprise In_(0.5)Ga_(0.25)Al_(0.25)P.

As a result of the fact that the first barrier layer starting from thep-type semiconductor region 4 is configured as a high barrier layer 73,the brightness of the optoelectronic semiconductor chip 10 at roomtemperature is reduced by about 17 percent in comparison with anotherwise identical optoelectronic semiconductor chip in which all thebarrier layers have the same electronic band gap. In the exemplifiedembodiment shown in FIG. 2, the relative decrease in brightness when thetemperature rises to 100° C. is about 40 percent instead of 50 percentin the case of a conventional semiconductor chip having barrier layerswith the same electronic band gap. Accordingly, in the exemplifiedembodiment the relative loss of brightness between room temperature andan operating temperature of 100° C. is advantageously reduced by 20percent in comparison with a conventional semiconductor chip.

Further advantageous embodiments and advantages of the optoelectronicsemiconductor chip 10 shown in FIG. 2 correspond to the firstexemplified embodiment and are therefore not described again in detail.

FIG. 3 shows a further exemplified embodiment of an optoelectronicsemiconductor chip 10 which is a modification of the exemplifiedembodiment of FIG. 1. The exemplified embodiment of FIG. 3 differs fromthe exemplified embodiment of FIG. 1 in that the two quantum well layers74 that adjoin the two high barrier layers 73 on a side facing towardsthe p-type semiconductor region 4 have an electronic band gap E_(lw)that is smaller than the band gap E_(w) of the other quantum well layers71. This is advantageous because it has been found that the high barrierlayers 73 give rise to an increased concentration of holes in thequantum well layers 74 adjoining in the direction of the p-typesemiconductor region 4. As a result of the high charge carrierconcentration in those quantum well layers 74, radiation-generatingcharge carrier recombinations also from more highly excited states takeplace, with the result that higher-energy radiation of shorterwavelength is emitted. That effect is reduced or even compensated as aresult of the fact that the electronic band gap E_(lw) of the quantumwell layers 74 that adjoin the high barrier layers 73 on a side facingtowards the p-type semiconductor region 4 is reduced in comparison withthe other quantum well layers 71. Further advantageous embodiments andadvantages of the optoelectronic semiconductor chip 10 shown in FIG. 3correspond to the first exemplified embodiment and are therefore notdescribed again in detail.

FIG. 4 shows a further exemplified embodiment of an optoelectronicsemiconductor chip 10 which is a modification of the exemplifiedembodiment shown in FIG. 2. The exemplified embodiment of FIG. 4 differsfrom the exemplified embodiment of FIG. 2 in that the quantum well layer75 that adjoins the high barrier layer 73 on a side facing towards thep-type semiconductor region 4 has a thickness d₂ that is greater thanthe thickness d₁ of the other quantum well layers 71. Increasing thethickness of the quantum well layer 75 adjoining the high barrier layer73 represents an alternative to the method shown in FIG. 3 of reducingthe emission wavelength of the radiation emitted in the quantum welllayer 75 in order to reduce or fully compensate an opposing effectcaused by charge carrier recombinations from more highly excited states.As regards further advantageous embodiments, the exemplified embodimentshown in FIG. 4 corresponds to the exemplified embodiment shown in FIG.2.

FIG. 5 shows the profile of the electronic band gap E_(g) in dependenceupon a spatial co-ordinate z running in the perpendicular direction in afurther exemplified embodiment of the optoelectronic semiconductor chip10. It is a semiconductor chip intended for emission at a wavelength of615 nm, which is based on the material system InGaAlP and, as in theexemplified embodiment shown in FIG. 2, has fifty layer pairs composedof alternating quantum well layers and barrier layers. The first barrierlayer starting from the p-type semiconductor region is in the form of ahigh barrier layer 73 which has a substantially larger electronic bandgap than the other barrier layers of the multiple quantum wellstructure. The function of the high barrier layer 73 and the advantagesarising therefrom correspond to the exemplified embodiments describedabove and are therefore not described again in detail here.

As an alternative to the exemplified embodiment shown in FIG. 5 it wouldalso be possible for the high barrier layer 73 to be arranged not afterthe first quantum well layer starting from the p-type semiconductorregion 4, but only after a plurality of quantum well layers. Inparticular, the high barrier layer 73 can be arranged between a quantumwell layer that is the m^(th) quantum well layer starting from thep-type semiconductor region and the immediately adjacent quantum welllayer, where m is a number between 1 and 20, preferably between 1 and10.

FIG. 6 shows the measured relative brightness B(T)/B(T=25° C.) for anoptoelectronic semiconductor chip according to a further exemplifiedembodiment (curve 12) in comparison with a conventional semiconductorchip (curve 13) in dependence upon the ambient temperature T. Theoptoelectronic semiconductor chip according to the exemplifiedembodiment is a light-emitting diode chip which is based on thesemiconductor material InGaAlP and has a multiple quantum well structurehaving 100 layer pairs composed of quantum well layers and barrierlayers, the first 10 barrier layers starting from the p-typesemiconductor region being configured as high barrier layers which havea larger electronic band gap than the other 90 barrier layers of themultiple quantum well structure. The comparison example of aconventional semiconductor chip is an otherwise identically constructedsemiconductor chip in which all 100 barrier layers have the sameelectronic band gap.

At a low temperature T, the high barrier layers of the exemplifiedembodiment of an optoelectronic semiconductor chip reduce the emittedbrightness, because the charge carrier transport of holes into the 90quantum well layers that follow the high barrier layers in the directiontowards the n-type semiconductor region is reduced. That effect declineswith increasing temperature T, because the charge carriers have greatermobility with increasing temperature and are accordingly able to passthrough the high barrier layers more easily. In the optoelectronicsemiconductor chip according to the exemplified embodiment, thebrightness therefore declines with increasing temperature to a lesserextent than in the case of the conventional semiconductor chip. Forexample, the decrease in brightness at a temperature T=100° C. is about7 percent less than in the case of a conventional semiconductor chip.

The description of the invention with reference to the exemplifiedembodiments does not limit the invention thereto; rather, the inventionencompasses any novel feature and any combination of features, includingin particular any combination of features in the patent claims, even ifthat feature or that combination is not itself explicitly defined in theclaims or exemplified embodiments.

What is claimed is:
 1. An optoelectronic semiconductor chip comprising: a p-type semiconductor region; an n-type semiconductor region; and an active layer suitable for emission of radiation arranged between the p-type semiconductor region and the n-type semiconductor region, the active layer comprising a multiple quantum well structure, the multiple quantum well structure having a plurality of alternating quantum well layers and barrier layers, wherein a barrier layer arranged closer to the p-type semiconductor region than to the n-type semiconductor region is a high barrier layer having an electronic band gap E_(hb) that is larger than electronic band gaps E_(b) of other barrier layers, and wherein a quantum well layer that adjoins the high barrier layer on a side of the high barrier layer facing towards the p-type semiconductor region has a thickness that is greater than thicknesses of other quantum well layers.
 2. The optoelectronic semiconductor chip according to claim 1, wherein the high barrier layer has a band gap E_(hb) for which the following applies: E_(hb)−E_(b)≥0.05 eV.
 3. The optoelectronic semiconductor chip according to claim 1, wherein the multiple quantum well structure has not more than 10 high barrier layers.
 4. The optoelectronic semiconductor chip according to claim 3, wherein first k barrier layers starting from the p-type semiconductor region are high barrier layers, where k is a number between 1 and
 10. 5. The optoelectronic semiconductor chip according to claim 1, wherein the multiple quantum well structure has just one high barrier layer.
 6. The optoelectronic semiconductor chip according to claim 5, wherein the high barrier layer is arranged between a quantum well layer that is a mth quantum well layer starting from the p-type semiconductor region and an immediately adjacent quantum well layer, where m is a number between 1 and
 20. 7. The optoelectronic semiconductor chip according to claim 6, wherein m=1.
 8. The optoelectronic semiconductor chip according to claim 1, wherein the multiple quantum well structure has a plurality of high barrier layers that are arranged closer to the p-type semiconductor region than to the n-type semiconductor region.
 9. The optoelectronic semiconductor chip according to claim 1, wherein the high barrier layer and the other barrier layers each comprise In_(x)Al_(y)Ga_(1-x-y)P or In_(x)Al_(y)Ga_(1-x-y)N, where 0≤x≤1, 0≤y≤1 and x+y≤1, and wherein an aluminum content y of the high barrier layer is greater than an aluminum content y of the other barrier layers.
 10. The optoelectronic semiconductor chip according to claim 1, wherein the high barrier layer and the other barrier layers each comprise In_(x)Al_(y)Ga_(1-x-y)As, where 0≤x≤1, 0≤y≤1 and x+y≤1, and wherein an aluminum content y of the high barrier layer is greater than an aluminum content y of the other barrier layers.
 11. The optoelectronic semiconductor chip according to claim 1, wherein the chip includes at least 10 other barrier layers.
 12. The optoelectronic semiconductor chip according to claim 11, wherein the chip includes at least 20 other barrier layers.
 13. The optoelectronic semiconductor chip according to claim 1, wherein the number of other barrier layers having the band gap E_(b) is at least 5 times as great as the number of high barrier layer(s) having the increased band gap E_(hb).
 14. The optoelectronic semiconductor chip according to claim 1, wherein the number of other barrier layers having the band gap E_(b) is at least 10 times as great as the number of high barrier layer(s) having the increased band gap E_(hb).
 15. The optoelectronic semiconductor chip according to claim 1, wherein a quantum well layer that adjoins the high barrier layer on a side facing towards the p-type semiconductor region has an electronic band gap E_(lw) that is smaller than a band gap E_(w) of other quantum well layers.
 16. The optoelectronic semiconductor chip according to claim 1, wherein the multiple quantum well structure is suitable for the emission of radiation in a wavelength range from 550 nm to 640 nm.
 17. An optoelectronic semiconductor chip comprising: a p-type semiconductor region; an n-type semiconductor region; and an active layer suitable for emission of radiation arranged between the p-type semiconductor region and the n-type semiconductor region, the active layer comprising a multiple quantum well structure, the multiple quantum well structure having a plurality of alternating quantum well layers and barrier layers, wherein a barrier layer arranged closer to the p-type semiconductor region than to the n-type semiconductor region is a high barrier layer having an electronic band gap E_(hb) that is larger than electronic band gaps E_(b) of other barrier layers, wherein a quantum well layer that adjoins the high barrier layer on a side facing towards the p-type semiconductor region has a thickness that is greater than thicknesses of other quantum well layers, wherein the multiple quantum well structure has just one high barrier layer, and wherein the high barrier layer is arranged between a quantum well layer that is a mth quantum well layer starting from the p-type semiconductor region and an immediately adjacent quantum well layer, where m is a number between 1 and
 20. 18. The optoelectronic semiconductor chip according to claim 17, wherein m=1. 